The prior art includes directional optical illuminators for eye-trackers. Such illuminators are advantageous relative to static ditto because, at each point in time, they only illuminate a fraction of a surface inside a volume within which the subject moves. Thereby, power is conserved corresponding to the size of the non-illuminated surface that would otherwise have been illuminated. US 2010/0066975 describes a solution, using a matrix-based illuminator with imaging optics, or a collimated beam, and a tiltable mirror to direct illumination towards the user of an eye-tracker.
Furthermore, diffractive optical elements (DOEs) are known, which are configured to transform a coherent light beam into an arbitrary intensity pattern. A brief DOE description is available via the URL http://www.rpcphotonics.com/optical.asp.
US 2004/0213463 reveals a solution for imaging and range detection, wherein a DOE-based technique is used for spatial encoding of light. Here, the position and shape of a light pattern can be changed instantly by inserting a different DOE into the light beam.
DOEs are sometimes also referred to as holographic optical elements. In such cases, the DOE often includes a phase mask, analog or digital, which is configured to transform a coherent light beam into a desired spatial pattern. The phase amplitude is typically less than one wavelength. It is also possible that the DOE includes an amplitude mask.